Cardiac cycle, ECG and action potentials Flashcards
How does blood flow through the heart?
Blood flows through the heart in the following sequence:
From the right atrium to the right ventricle.
Then through the pulmonary arteries to the lungs for oxygenation.
From the left atrium to the left ventricle.
Finally, it flows through the aorta to the rest of the body.
The flow direction is determined by the pressure and the presence of valves in the heart.
What are the types of valves in the heart and their functions?
Atrioventricular valves: These include the tricuspid valve on the right side and the bicuspid (mitral) valve on the left side. They prevent backflow of blood into the atria.
Semilunar valves: These include the pulmonary valve (which directs blood to the lungs) and the aortic valve (which directs blood to the body).
What is the electrochemical gradient in cardiac cells?
The electrochemical gradient refers to the separation of charge across the cell membrane, where the inside of the cell is more negatively charged compared to the outside. This gradient is created by the distribution of sodium (Na+) and potassium (K+) ions. The membrane potential is closer to repolarization due to a higher concentration of potassium ions, but it becomes depolarized when sodium ions enter the cell, causing a positive charge inside the cell.
What is the role of calcium ions in heart muscle contraction?
When calcium ions enter the cardiac cells, they bind to troponin, which causes the exposure of the myosin-binding sites on actin. This initiates the formation of actin-myosin cross-bridges, leading to muscle contraction in the heart.
How does electrical impulse spread in the heart during contraction?
The electrical impulse in the heart spreads as follows:
The Sinoatrial (SA) node initiates the electrical impulse.
The impulse spreads across the atria and reaches the Atrioventricular (AV) node.
A 100 millisecond delay occurs at the AV node to allow the ventricles to fill.
The impulse then travels through the Atrioventricular bundle and bundle branches to the Purkinje fibers.
Finally, the impulse is distributed throughout the ventricular myocardium, leading to ventricular contraction.
- What are the key components of the heart’s conduction system?
What are the key components of the heart’s conduction system?
Sinoatrial (SA) node: The initiator of the electrical impulse.
Atrioventricular (AV) node: Acts as a delay node, allowing for ventricular filling.
Bundle branches: Electrical conduction pathways through the left and right myocardium, including the bundle of His.
Purkinje fibers: Specialized cells responsible for translating the electrical impulse into contractile force in the ventricles.
What is an electrocardiogram (ECG), and what does it measure?
An ECG (electrocardiogram) measures the electrical activity of the heart. It typically uses 12 leads from 10 points on the chest to record the electrical depolarizations and repolarizations of the heart’s atria and ventricles.
What do the different waves on an ECG represent?
P wave: Represents atrial depolarization (contraction of the atria).
QRS complex: Represents ventricular depolarization (contraction of the ventricles).
T wave: Represents ventricular repolarization (relaxation of the ventricles).
What is the importance of the delay at the AV node in the conduction process?
The delay at the AV node (about 100 milliseconds) is crucial because it allows for atrial contraction to finish before the ventricles contract. This ensures that the ventricles fill completely with blood before they begin to pump it to the lungs and body.
What happens during the depolarization of cardiac cells?
During depolarization, sodium ions (Na+) flow into the cardiac cells, making the inside of the cell more positively charged compared to the outside. This change in membrane potential leads to the initiation of a contraction in the heart muscle.
How does the heart muscle ensure synchronized contraction?
The heart muscle ensures synchronized contraction by transmitting electrical impulses through gap junctions in the intercalated disks between cardiac cells. This allows the electrical depolarization to spread rapidly from one cell to another, resulting in coordinated contraction of the heart muscle.
What is the role of the moderator band in the conduction system?
The moderator band is a structure in the right ventricle that helps to transmit the electrical impulse from the bundle branches to the papillary muscles, ensuring coordinated contraction of the ventricle and proper valve function.
Why is the 100 millisecond delay at the AV node important?
The 100 millisecond delay at the AV node is important because it allows time for the atria to contract and fully fill the ventricles with blood before the ventricles contract. This ensures efficient ventricular filling and optimal blood flow.
How do calcium ions contribute to muscle contraction in the heart?
Calcium ions bind to troponin on the actin filaments of the heart muscle. This binding exposes the myosin-binding sites on actin, enabling the formation of actin-myosin cross-bridges and initiating muscle contraction.
What would happen if the sinoatrial (SA) node were damaged?
If the SA node were damaged, the heart would lose its natural pacemaker function. Another part of the conduction system, such as the AV node, may take over as a secondary pacemaker, but the heart rate would typically be slower than normal. An artificial pacemaker may be required to regulate heart rhythm.
What is the resting membrane potential in cardiac cells, and why is it important?
The resting membrane potential in cardiac cells is typically negative, meaning the inside of the cell is more negative compared to the outside. This potential difference is important because it allows the heart muscle cells to be ready for depolarization and subsequent contraction when stimulated by an electrical impulse.
How do autorhythmic cells differ from contractile cells in the heart?
Autorhythmic cells are specialized cells in the heart, primarily located in the SA node, that generate their own electrical impulses automatically (without external stimulation) and control the heart’s rhythm. In contrast, contractile cells are responsible for muscle contraction in the heart and respond to the electrical impulses generated by autorhythmic cells.
How does the heart ensure blood flow to the body and lungs during contraction?
During ventricular contraction, the semilunar valves (pulmonary and aortic valves) prevent blood from flowing back into the ventricles. The pressure created by the contraction forces blood into the pulmonary arteries (to the lungs) and the aorta (to the body).
